Advances in polymer chemistry and technology over the last few decades have enabled the development of high-performance polymeric fibers. For example, liquid-crystalline polymer solutions of rigid-rod polymers can be formed into high strength fibers by spinning liquid-crystalline polymer solutions into dope filaments, removing solvent from the dope filaments, washing and drying the fibers; and if desired, further heat treating the dried fibers to increase tensile properties. One example of high-performance polymeric fibers is para-aramid fiber such as poly(paraphenylene terephthalamide) (“PPD-T” or “PPTA”).
Fibers derived from 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI), para-phenylenediamine (PPD) and terephthaloyl dichloride (TCl) are known in the art. Hydrochloric acid is produced as a by-product of the polymerization reaction. The majority of the fibers made from such copolymers have generally been spun directly from the polymerization solution without further treatment. Such copolymers are the basis for high strength fibers manufactured in Russia, for example, under the trade names Armos® and Rusar®. See, Russian Patent Application No. 2,045,586. However, the copolymer can be isolated from the polymerization solvent and then redissolved in another solvent, typically sulfuric acid, to spin fibers, as provided for example, in Sugak et al., Fibre Chemistry Vol 31, No 1, 1999; U.S. Pat No. 4,018,735; and WO 2008/061668.
Known processes for making copolymer fibers directly from polymerization solution, while producing a good product for use in ballistic and other aramid end-uses, are very expensive with very poor investment economics. As such, there is a need in the art for manufacturing processes wherein the copolymer is solutioned in a common solvent, such as sulfuric acid which has improved economics compared to processes known in the art.
Previously, it has been assumed that fibers derived from copolymers of 5(6)-amino-2-(p-aminophenyl)benzimidazole, para-phenylenediamine and terephthaloyl dichloride and solutioned from sulfuric acid could be spun into to high quality fibers using processing similar to that used for making PPD-T fibers, since the compositions appear similar. However, it has been found that spinning the copolymer into high tenacity fibers has unique challenges that are not present in the PPD-T framework and new techniques are needed. Since higher tenacity fibers can provide more utility due to their strength per unit weight, improvement in tenacity is welcomed.